Synthesis of Porphyrin-Dendrimers with a Pyrene in the Periphery and Their Cubic Nonlinear Optical Properties

Abstract

Dendrons of pyrene derivatives were attached to a porphyrin core. A marked effect in solution for the dendrimers was observed in the absorption spectra. All the compounds obtained were characterized by 1H-, 13C-NMR, FTIR, UV-vis, MALDI-TOF or FAB+ mass spectrometry and elemental analysis. The cubic nonlinear optical behavior of some the synthesized compounds was tested via Z-Scan measurements in spin-coated film samples.

Internal Dynamics of Dendritic Molecules Probed by Pyrene Excimer Formation

“…One major advantage of Equation (16) is that the emission due to free pyrene labels can be isolated so that the true I E /I M ratio of a pure pyrene-labeled dendrimer is obtained simply by setting f free in Equation (16) to equal zero to yield ⁄ . In turn, ⁄ is expected to be proportional to the average rate constant of pyrene excimer formation <k> defined hereafter, as has been found in a number of studies [73,74,78,125,126,176]. A discrepancy between ⁄ and <k> would imply that something is amiss in the analysis.…”

“…However, out of the eight reports presenting data on pyrene-labeled [36,37,44,[120][121][122][123][124][125], only two [44,120] present some information about the process of pyrene excimer formation, in particular via the ratio (I E /I M ) SS . Stewart and Fox [120] chose a 1-pyrenylbenzylether substituent to label a first generation dendrimer (see chemical structure in Table 1) whereas Cicchi et al [44] chose a 1-pyrenebutyltriazol moiety to label generations 1-3 of their poly(benzyl ether) dendrimers (Table 1).…”

“…Over the years, the synthesis of several pyrene-labeled dendrimers has been reported in the literature [36,37,44,[120][121][122][123][124][125][126][127][128][129][130][131][132][133][134], but in many instances, the pyrene-labeled constructs were synthesised as pyrene-labeled dendrons to be attached onto a focal point bearing an acceptor molecule capable of communicating with the pyrenyl pendants [36,44,[120][121][122][123]. Consequently, these investigations focused on the photophysical process taking place between the pyrene donor and the acceptor rather than on excimer formation between pyrene pendants covalently attached to the chain ends of dendrimers.…”

“…Fluorescence resonance energy transfer (FRET), energy hopping or migration, and electron transfer between a donor and an acceptor are all photophysical processes whose efficiency depends strongly on the distance between the donor and acceptor [135][136][137]. The design of dendrimers used for this type of applications consists in placing many donors at the dendrimer periphery and a single acceptor molecule at the dendrimer focal point [3,36,[39][40][41][42][43][44][120][121][122][123]125]. As the dendrimer generation increases, the efficiency of the photophysical process of interest decreases according to the increased distance separating the donor from the acceptor [135][136][137].…”

“…Interestingly, whereas the study of the pyrene excimer formation of pyrene-labeled linear polymers has been astonishingly successful at characterizing the internal dynamics of these macromolecules [73][74][75], much fewer pyrene-labeled dendrimers have been prepared to study intramolecular excimer formation [117][118][119][120][121][122][123][124][125][126][127][128][129][130][131][132][133][134]. Surprisingly for such a rather small set of studies, many of these studies yield trends that are, in the opinion of the author, both internally and externally inconsistent and which, if taken at their face value, would lead the non-expert in fluorescence to the erroneous conclusion that pyrene excimer formation cannot be successfully applied to characterize the internal dynamics of dendrimers.…”